Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

505
FXUS63 KLOT 141122
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
522 AM CST Sun Dec 14 2025

.KEY MESSAGES...

- Dangerous cold with sub-zero wind chills continues through
  Monday morning.

- Some blowing and drifting snow, particularly on east to west
  roadways, late tonight into Monday for areas that received
  several inches of fluffy snow on Saturday.

- Moderating temperatures expected through Thursday.

- Period of rain showers Wednesday night-Thursday, followed by
  blustery conditions and briefly colder conditions Thursday
  night and Friday.

&&

.DISCUSSION...
Issued at 245 AM CST Sun Dec 14 2025

Through Monday:

Arctic high pressure currently analyzed at 1042 hPa along the
Missouri River Valley will pass southwest of the forecast area
this afternoon and evening. Gradually dissipating and descending
upper-level clouds will filter in from the northwest late in
the day and this evening, but sunny skies will prevail for much
of the day. Even with the abundant sunshine, temps will struggle
to reach the teens this afternoon outside of the core of the
Chicago metro and downwind of Lake Michigan in northwest
Indiana. Wind chill values will settle in the -20 to -25F range
by sunrise amid persistent NW winds of 10 to 15 mph. Winds chill
should then slowly rise back to the 0 to -10F range for the
afternoon as wind speeds slightly diminish. Have maintained the
Cold Weather Advisory that runs through noon CST.

Scattered lake effect snow showers will continue through early
afternoon for northeast Porter County. Thermo profiles will
become most favorable over the next six hours or so as much of
the convective layer resides in the DGZ. However, current
inversion heights around 5kft will quickly lower to under 3kft
by mid-afternoon. Overall, a fluffy 1-2" of accumulation is
possible through the morning hours.

West winds this evening will back SW overnight while increasing
between the departing surface high and 1012 hPa trough crossing
Lake Superior. A 60 knot LLJ will maximize over the forecast
area around sunrise Monday before quickly sliding southeast
through the day. It is expected that the surface layer will
decouple overnight in response to increased mixing as the LLJ
nears, resulting in a slow rise in air temps after midnight.
Initial wind chill values in the -10 to -20F range this evening
will likely hold steady or slightly rise as warming temps
counter increasing winds overnight. This precludes the need for
an additional Cold Weather Advisory (-20F or colder) tonight as
long as temps do not trend further to the downside this evening.

Finally, with yesterday`s system leaving a fluffy snow pack
across the southern CWA, there is some concern that the surge in
winds late tonight into Monday will result in plenty of blowing
and drifting snow across E/W roads in open/rural areas. Have
included this mention in the forecast for areas roughly along
and south of a line from Streator to Kankakee to Rensselaer.

Kluber


Monday Night through Saturday:

A secondary surface high will build into the region Monday
night. As this occurs, winds will ease allowing temperatures to
fall into the teens. With the increase in dewpoints on Monday,
this could set the stage for at least some shallow fog
development into Tuesday morning as temperatures fall below
their crossover values. Some lingering flow just off the surface
could be a bit of a mitigating factor, and as a result, have
not introduced a mention into the gridded forecast at this time.

On Tuesday, a compact but intense shortwave will shift east
across the Minnesota Arrowhead Region. This will eventually
help send a modest cold front through the CWA Tuesday night.
While the most significant height falls are forecast to remain
north of the area, 50 to 80 m/12 hour 500 mb height falls will
spread across northern Illinois. While all deterministic
guidance remains dry, seeing some splotches of very light precip
in some of the ensemble guidance ahead of the front. The main
hangup seems to be tied to a modeled dry sub-cloud layer
(900-700 mb). At this time, the general multi-model consensus
remains decidedly dry, but will continue to keep an eye on this
time frame due to the presence of somewhat steep mid-level
lapse rates. Concern would be if precipitation materializes, it
would possibly be liquid due to a significant warm nose aloft,
and ground temperatures would likely still be sub-freezing
coming out of our arctic snap. Altogether, not seeing anything
overly concerning at this point, however.

Blustery northwest winds Wednesday morning will quickly be
replaced by strengthening southerly flow Wednesday evening and
overnight as the next robust disturbance approaches and
encourages a deep surface low eastward across the Upper Great
Lakes. Substantial height falls/DCVA look set to drive a rapid
expansion of showers across the local area Wednesday night into
early Thursday morning. Surface dewpoints look to surge above
freezing prior to the development of the bulk of this
precipitation, with wetbulb temperatures commensurately rising
through the 30s and lower 40s, so no concerns with frozen precip
with this round.

A strong cold front will push through the area on Thursday.
Depending on how quickly the column cools, suppose there`s a
brief potential for a little snow to mix in prior to precip
shutting off, but this doesn`t look consequential at this point.
Strong CAA and steepening low-level lapse rates will promote a
period of strong westerly winds Thursday afternoon and night,
potentially gusting over 40-45 mph at times. This will be
followed by temperatures falling back into the teens and
possibly single digits by Friday morning.

Carlaw

&&

.AVIATION /12Z TAFS THROUGH 18Z MONDAY/...
Issued at 522 AM CST Sun Dec 14 2025

Gusts will diminish this morning, with northwesterly winds
around 10 kt prevailing today before shifting out of the
southwest late this afternoon. A region of MVFR stratus
continues to make southward progress through east-central
Wisconsin. At this time, it doesn`t look like this lower cloud
cover will make it to the terminals. At GYY, lake effect snow
showers are expected to remain east of the terminal, but some
could push just within the 10 mile ring later this morning.

A strong LLJ will develop late tonight. In response, south-
southwesterly winds will increase and should become at least
intermittently gusty late tonight. Even with the addition of
gusts, southwesterly winds around 50-55 kts at 2 kft will lead
to a brief period of LLWS before surface winds and gusts
increase mid-late Monday morning.

Carlaw

&&

.MARINE...
Issued at 245 AM CST Sun Dec 14 2025

West winds this evening will back southwest overnight and
quickly increase as a 60 knot low-level jet passes over
southern lake Michigan around sunrise Monday. The low-level jet
will sit atop a stout inversion as low as 1kft, with the
existing arctic airmass yielding unstable conditions over the
nearshore waters. There remains some uncertainty as to whether
the shallow unstable layer below the strong inversion will be
able to mix into the much stronger winds aloft (and for how
long). Have maintained a Gale Watch for late tonight through
Monday morning as southwest gales 35 to 40 knots remain
possible, but may ultimately be short-lived, infrequent, and/or
only at the highest platforms.

Kluber

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Cold Weather Advisory until noon CST today for ILZ003-ILZ004-
     ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-ILZ013-ILZ019-
     ILZ020-ILZ021-ILZ023-ILZ032-ILZ033-ILZ039-ILZ103-ILZ104-
     ILZ105-ILZ106-ILZ107-ILZ108.

IN...Cold Weather Advisory until noon CST /1 PM EST/ today for
     INZ001-INZ010-INZ011-INZ019.

LM...Small Craft Advisory until noon CST today for Winthrop Harbor
     IL to Gary IN.

     Gale Watch from late tonight through Monday morning for the IL
     and IN nearshore waters.

     Small Craft Advisory until 9 PM CST this evening for Gary to
     Burns Harbor IN-Burns Harbor to Michigan City IN.

&&

$$

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